We have been studying the physiology of the gastrointestinal system for a number of years. Our major emphasis has been on pancreatic function, studying both electrolyte and digestive enzyme secretion. We have been interested in both mechanisms of secretion and the regulation of the secretory process. To study salt and water secretion we have used a preparation of whole secreting rabbit pancreas in vitro, and more recently, small strips of rabbit pancreas also in vitro, both of these techniques developed by Dr. Rothman. The strip preparation has made it possible for us to study unidirectional fluxes across both serosal and ductal surfaces of the pancreatic secretory cell virtually simultaneously, thereby permitting an analysis of the detailed events involved in the secretory process and its regulation by hormones. Our studies on protein secretion have followed two separate lines; one examining the regulation of protein synthesis and secretion by making use in part of feeding trypsin inhibitor-containing diets to rats and also performing acute in situ experiments with perfused intestinal loops. The other direction has been to examine the intimate mechanisms involved in the secretory process particularly those of intracellular transport of digestive enzyme and the assembly and secretion of the zymogen granule.